A planetary gear comprises a planet carrier, a sun shaft, a gear ring, and planet wheels meshing with the sun shaft and with the gear ring. The planet wheels are supported with planet shafts which, in turn, are supported by the planet carrier. Bearings of the planet wheels can rolling-bearings or slide-bearings. An advantage of slide-bearings with respect to rolling-bearings is that slide-bearings require less room in the radial direction and the load carrying surfaces of slide-bearings are larger than those of rolling-bearings. A challenge related to slide-bearings is that they are prone to being damaged during assembly of a planetary gear.
Publication EP2847497 describes a planetary gear comprising planet wheel assemblies based on slide-bearings. Each planet wheel assembly comprises two bushings fixedly connected to a planet shaft. Each of the bushings is L-shaped in the cross-section and has a radial contact surface and an axial contact surface. The bushings are mounted to form a cross-sectional U-shape so that the axial contact surfaces of the bushings are facing towards each other and at least part of a planet wheel is located within the U-shape formed by the L-shaped bushings. The bushings are locked in the axial direction at both outer sides by abutments constituted by a planet carrier. The planet wheel assembly further comprises a radial sliding element between the radial contact surface of each bushing and a respective radial contact surface of the planet wheel, and an axial sliding element between the axial contact surface of each bushing and a respective axial contact surface of the planet wheel. The radial and axial sliding elements can be first mounted on the bushings, and thereafter the resulting assemblies can be placed into the hole of the planet wheel. When the planet shaft is pushed through the holes of the bushings, the radial and axial sliding elements are protected by the bushings and thus the damaging risk of the radial and axial sliding elements is reduced.
The planetary gear described in the publication EP2847497 is, however, not free from challenges. One of the challenges is related to the fact that axial rooms required by axial slide-bearings shorten the axial length available for radial slide-bearings because each radial slide-bearing is located within the above-mentioned U-shape formed by the L-shaped bushings. This limits the ability of the radial slide-bearings to act against forces tending to tilt the geometric rotational axis of the planet wheel with respect to the planet shaft.